Differentiation and quantification of synthetic phosphatidylethanol (PEth) homologues by ¹H- and ¹³C-NMR in polar organic solvents.

Various phosphatidylethanol (PEth) derivatives, the corresponding reversed positional isomers (RPI-PEths), lyso-PEth-16:0, and penta-deuterium-labeled PEth analogs (d5-PEths), were synthesized by enzyme-independent synthetic routes. A general solvent system consisting of a mixture of acetone-d6 and methanol-d4 (97:3; v/v) was found to provide a good solubilizing capacity and excellent hydrogen-1 NMR ((1)H-NMR) peak resolution of various PEth homologues. Analytical differentiation of PEth from the corresponding RPI-PEth by carbon-13 NMR ((13)C-NMR) was demonstrated by comparison of the (13)C-NMR signals of the carbonyl groups, the allylic positions, and of the ß-carbons. An exemplary stable long-term room temperature, DMSO-d6-based, and proton-sensitive quantitative nuclear magnetic resonance ((1)H-qNMR) independently quantified calibrator comprising PEth-16:0/18:1 for liquid chromatography (tandem) mass spectrometry (LC-MS/MS) analytical applications were prepared by employment of sodium dodecyl sulfate (SDS) as a solubilizing additive. In summary, novel hypothetically occurring PEth derivatives, e.g., RPI-PEths, have been independently synthesized with regio- and stereochemical control. Use of polar organic solvents, e.g., mixtures of acetone-d6 and methanol-d4 or DMSO-d6, improves spectral line shapes as compared to traditional hydrophobic solvents and allow for analytical differentiation between closely related PEth derivatives, as well as LC-MS/MS-independent concentration determination of dissolved single species by employment of (1)H-qNMR.

Efficient chemoenzymatic dynamic kinetic resolution of 1-heteroaryl ethanols.

The scope and limitation of the combined ruthenium-lipase induced dynamic kinetic resolution (DKR) through O-acetylation of racemic heteroaromatic secondary alcohols, i.e., 1-heteroaryl substituted ethanols, was investigated. After initial screening of reaction conditions, Candida antarctica lipase B (Novozyme 435, N435) together with 4-chloro-phenylacetate as acetyl-donor for kinetic resolution (KR), in conjunction with the ruthenium-based Shvo catalyst for substrate racemization in toluene at 80 degrees C, enabled DKR with high yields and stereoselectivity of various 1-heteroaryl ethanols, such as oxadiazoles, isoxazoles, 1H-pyrazole, or 1H-imidazole. In addition, DFT calculations based on a simplified catalyst complex model for the catalytic (de)hydrogenation step are in agreement with the previously reported outer sphere mechanism. These results support the further understanding of the mechanistic aspects behind the difference in reactivity of 1-heteroaryl substituted ethanols in comparison to reference substrates, as often referred to in the literature.